Abstract
The Belle II experiment is a high energy multi purpose particle detector operated at the asymmetric e + e − - collider SuperKEKB in Tsukuba (Japan). In this work we describe the algorithm performing the pattern recognition for inner tracking detector which consists of two layers of pixel detectors and four layers of double sided silicon strip detectors arranged around the interaction region. The track finding algorithm will be used both during the High Level Trigger on-line track reconstruction and during the off-line full reconstruction. It must provide good efficiency down to momenta as low as 50 MeV/c where material effects are sizeable even in an extremely thin detector as the VXD. In addition it has to be able to cope with the high occupancy of the Belle II detectors due to the background. The underlying concept of the track finding algorithm, as well as details of the implementation are outlined. The algorithm is proven to run with good performance on simulated ϒ(4S ) → BB events with an efficiency for reconstructing tracks of above 90% over a wide range of momentum.
Highlights
350 MeV/c and with the high occupancy (1.5%) foreseen in the inner silicon layers will challenge the sub-detectors of Belle II and the track finding algorithms.Track position information close to the interaction point is provided by the vertex detector (VXD) which consists of 2 layers of pixel detectors (PXD) and 4 layers of double sided silicon strip vertex detectors (SVD) whose overall thickness and dead material is kept at a minimum to reduce the effects of multiple Coulomb scattering.The track finding code for the VXD of Belle II implements in an efficient way the Sector Map concept originally proposed by Rudolf Frühwirth and originally implemented by Jakob Lettenbichler [1].The typical event recorded by the VXD will be dominated by random hits produced by beam background
The PXD is surrounded by the Silicon Vertex Detector (SVD) [5] which consists of 4 layers of double sided silicon strip detectors positioned at radii of 38 mm, 80 mm, 115 mm, and 140 mm from the interaction point
The track finding efficiency for the algorithm at hand is evaluated as the fraction of the number of “good” tracks found by the pattern recognition algorithm described so far over the number of track candidates found by the ITF
Summary
350 MeV/c and with the high occupancy (1.5%) foreseen in the inner silicon layers will challenge the sub-detectors of Belle II and the track finding algorithms. The typical event recorded by the VXD will be dominated by random hits produced by beam background (order of 500 pixels hit per event per sensor on the inner layer of the PXD, 20 GByte/s required to readout the whole PXD). The track finding algorithm presented here will be used both during the final reconstruction of the event and during the fast reconstruction occurring on the High Level Trigger (HLT) for the definition of the Regions Of Interest on the PXD sensors used to reduce the PXD data stream to a manageable level [2] This latter task put tight constraints on the reliability and time consumption of the track finding algorithm since an eventual crash or malfunction of the HLT process will immediately translate in a permanent loss of data and since the time left for the silicon vertex identification is in the ball park of a few milli-seconds per event. This paper presents the main concepts of the algorithm, some details of its implementation together with its current performances
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
